textproduct: Rapid City

KEY MESSAGES

- Marginal to Slight (Level 1-2 out of 5) risk of severe thunderstorms this afternoon/evening with the primary risk of damaging winds, but large hail may also occur.

- After "cooler" temperatures today and Friday, very hot weather returns for the weekend with the hottest day Sunday.

- Elevated (Saturday) to critical (Sunday) fire weather conditions expected this weekend.

DISCUSSION

(This Afternoon Through Wednesday) Issued at 1105 AM MDT Thu Jul 30 2026

16z surface analysis had weak low over the NE panhandle with a boundary into central SD per 0.5km 1-minute visible satellite loop. Cold front was located from western ND into western WY. Water vapour loop had shortwave trough over northern WY with 80kt jet streak. These features starting to force CU/TCU/TS along the surface boundary with evidence of decent lift ahead of the shortwave over northeastern WY/eastern MT. Concern this afternoon/evening is severe weather.

This afternoon/evening, shortwave trough moves east as convergence along the surface boundaries increase. Mid-level flow increases effective shear to 25-35kts with locally higher amounts over central SD. Strong buoyancy will develop this afternoon, especially east of the Black Hills. Initial storm mode may be cellular with large hail potential, but the trend will be toward severe clusters/linear severe convection as storm cold pools congeal. Primary threat will be damaging winds gusts (70+ mph). Looking for a fairly early start this afternoon with CAMs focusing on the central/southern Black Hills and central SD this afternoon and then Lemmon to Winner by evening as the main shortwave wraps through the CWA. PWATs will be 150-200% of normal east of the Black Hills, so locally heavy rain and potential flash flooding may occur. Activity wanes overnight. Temperatures will be near guidance.

A weak shortwave moves through Friday, but drier air will be filtering into the CWA, so PoPs should be limited to our higher terrain areas.

Hot to very hot weather returns for the weekend with the preponderance of ensemble guidance giving highs near 110F for some folks Sunday. Much drier air in place, so thunderstorm chances will be unmentionable. Cooler weather returns Monday with actual "cool" air in place for the middle of next week per flattening upper ridge and west/northwest flow aloft for the northern Plains.

AVIATION

(For the 00Z TAFS Through 00Z Friday Evening) Issued At 600 PM MDT Thu Jul 30 2026

Thunderstorm chances have likely ended for the night at KGCC and KRAP, with a line of gusty storms continuing to track east across most of our South Dakota plains. Brief drops to MVFR and gusty/erratic winds to 40kts will be possible with this line as it continues east through about 05z/11pm. Behind it, strong northwest winds will impact KRAP for the next several hours as a front crosses the area, with gusts to 30kts. Outside of thunderstorms, VFR conditions are expected. Moving into tonight, our South Dakota plains may get fairly moist with several sources of guidance projecting RH values over 90 percent, but little support exists at this time for fog (including NBM/HRRR/MOS vsby output). Some low stratus will be possible through east of KRAP, perhaps to MVFR. Finally, for Friday...VFR conditions are currently forecast. Some potential for isolated thunderstorms exists during the afternoon, but consensus on coverage, timing, and placement across the CAMs is very poor at this time with a couple of them staying almost completely dry. Will watch updates as we go forward to see if better agreement emerges and whether a PROB30 is needed at either KGCC or KRAP.

FIRE WEATHER

Issued At 1105 AM MDT Thu Jul 30 2026

Strong/severe thunderstorms are expected this afternoon/evening with strong gusty, erratic winds as the primary threat. Elevated (Saturday) to critical (Sunday) fire weather conditions are expected this weekend. Minimum relative humidity will drop into the upper single digits/teens Saturday in the west and Sunday over much of the area. Winds Saturday will be marginally gusty for critical Fire Weather, but should be more robust on Sunday per very deep boundary layer mixing.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.